辽东台隆、燕山带和兴蒙造山带台站下方地壳厚度和平均波速比(VP/VS)的横向变化及其构造意义

本文研究采用接收函数H-κ方法获得了辽东台隆、燕山带和兴蒙造山带台站下方的地壳厚度和平均波速比(VP/VS).结果显示,研究区域三个构造区地壳平均厚度略有差别,分别为32、33 km和35 km,但横向变化特征各异.辽东台隆地壳中间厚两端薄,燕山带地壳厚度的变化相对平缓,而在兴蒙造山带内,以索伦缝合带为界地壳呈由东南向...

Transverse variations of crustal thickness and VP/VS ratio under the stations in the Liaodong anteclise-Yanshan belt-Xingmeng orogenic belt and their tectonic implications

We obtained the crustal thickness and average crustal V_P/V_S ratio along the profiles across the Liaodong anteclise, Yanshan belt and Xingmeng orogenic belt using H-κ stacking of receiver functions. The result shows that the average crustal thicknesses of these three tectonic units are 32, 33 and 35km, respectively, indicative of slight differences, and display distinct transverse variations in the crustal structure. The crust is thicker in the middle and thinner on each side in the Liaodong anteclise, whereas the thickness of the crust varies smoothly in the Yanshan belt. In the Xingmeng orogenic belt, the crust thickens sharply from southeast to northwest near the Solonker suture. The V_P/V_S ratio also fluctuates obviously in the study region. In particular, it varies laterally in the Yanshan belt and increases markedly nearby the boundary area between the Yanshan belt and the Xingmeng orogenic belt (near the north-south gravity lineament (NSGL)). However, the V_P/V_S ratio is relatively low and has no much change in the Xingmeng orogenic belt. The distinct crustal structures between the Yanshan belt and the Xingmeng orogenic belt are probably indicative of a more intense crustal modification in the Yanshan belt compared with the Xingmeng orogenic belt during Mesozoic-Cenozoic time. Significant changes in the crustal structure roughly coincide with the NSGL. This together with the concordant change in the deep lithospheric structure observed previously suggests that the NSGL may be a lithospheric-scale intra-continental tectonic boundary, the opposite sides of which may have evolved differently in the Phanerozoic. The thickening of the crust in the Xingmeng orogenic belt (near the Solonker suture) and the Liaodong anteclise appears to mirror the surface topography, and corresponds to relatively stable V_P/V_S ratios. This feature probably indicates relatively even Phanerozoic modifications of the crust in each region, resulting in minor lateral variations in the crustal structure and components at the present time.